Referring to FIG. 5 to FIG. 8, description of conventional types of angular velocity sensors as disclosed in Patent Literature 1 will be given. FIG. 5 is a top view of a conventional angular velocity sensor and FIG. 6 is an enlarged plan view of part A in FIG. 5. FIG. 7 is a sectional view taken along line 7-7 in FIG. 6. FIG. 8 is a perspective view of a conventional angular velocity sensor.
As shown in FIG. 5, a conventional angular velocity sensor comprises frame-shaped fixed part 1 and weight 10 coupled inward of fixed part 1 through flexible part 2. Flexible part 2 has at least one bending part 2A. Also, as shown in FIG. 6, conventional angular velocity sensor 2 has first electrode 3 disposed on the outside and second electrode 4 disposed on the inside at bending part 2A. As shown in FIG. 7, first electrode 3 and second electrode 4 are so structured that piezoelectric layers 3C, 4C are sandwiched between upper electrodes 3A, 4A and lower electrode 3B, 4B, respectively. Here, third electrode 15 disposed between first electrode 3 and second electrode 4 is a wiring electrode to be connected with an electrode for detecting acceleration and has the same structure as that of first electrode 3 and second electrode 4.
Low accuracy of detection of conventional angular velocity sensors having such a structure has been a problem for the reason described below.
In the conventional structure as shown in FIG. 6, as the electrodes are made with the same width, the area of first electrode 3 disposed on the outside becomes greater by necessity than the area of second electrode 4 disposed on the inside. Accordingly, as shown in FIG. 8, even in the event of a force being applied to weight 10 in a direction perpendicular to fixed part 1, the amount of electric charges generated due to distortion of piezoelectric layer 3C at first electrode 3 shown in FIG. 7 becomes greater than the amount of electric charges generated due to distortion of piezoelectric layer 4C in second electrode 4. As a result, erroneous detection has been made that the angular velocity around an axis perpendicular to fixed part 1 had occurred rather than in the direction perpendicular to fixed part 1.
That is, the angular velocity around an axis perpendicular to fixed part 1 is originally to be detected by subtracting the sum of the electric charges generated at lower electrode 3B of first electrode 3 and the electric charges generated at upper electrode 4A of second electrode 4 from the sum of the electric charges generated at upper electrode 3A of first electrode 3 shown in FIG. 7 and the electric charges generated at lower electrode 4B of second electrode 4.
However, in the case a force is applied in a direction perpendicular to fixed part 1, the electric charges generated at upper electrode 3A and lower electrode 4B shown in FIG. 7 are not cancelled each other, nor are the electric charges generated at upper electrode 4A and lower electrode 3B cancelled each other. Accordingly, the amount of electric charges due to distortion of piezoelectric layer 3C in first electrode 3 disposed on the outside of bending part 2A is greater than the electric charges generated due to distortion of piezoelectric layer 4C in second electrode 4 disposed on the inside of bending part 2A.
For the above reasons, with conventional angular velocity sensors, even in the case a force is applied to fixed part 1 in a perpendicular direction, erroneous detection is made that angular velocity around an axis perpendicular to fixed part 1 was generated, thus resulting in lowered accuracy.    [Patent Literature 1] Unexamined Japanese Patent Publication No. 2005-3588